Ozone is an allotropic form of oxygen containing three oxygen atoms per molecule. It is an extremely powerful oxidizing agent with the oxidation-reduction potential being 2.7 volts. Ozone reacts with a large number of organic compounds in aqueous and nonaqueous environments. Since ozone decomposes rapidly, its application in the destruction of organic waste is limited unless it is introduced continuously. The stability of aqueous ozone, however, can be improved by several methods which include lowering the solution pH or increasing the concentration of base in high pH environments. Ozone half-life values in 0.05 M phosphate buffer solutions at pH 4 and 10 are approximately 10,000 and 10 seconds, respectively. Hoigne and Bader; Hoigne, J., and Bader, H., 1983, Rate Constants of Reactions of Ozone with Organic and Inorganic Compounds in Water-I, Water Research, Vol. 17, pp. 173-183; reported that the addition of sodium bicarbonate and dimethyl mercury increased the stability of ozone at high pH. An increase in base (NaOH) concentration from 1 N to 20 N also results in the extension of the half-life of ozone by more than three orders of magnitude. However, such high base concentrations or application of chemicals such as methyl mercury are not practical for on-site treatment of contaminated soil.
In most of the previous work, ozone has been used to destruct or treat organic wastes present in aqueous media (U.S. Pat. Nos.: 2,703,247; 3,920,547; 4,029,578; 4,076,617; 4,098,691; 4,487,699; 4,537,599; 4,619,763; Japanese Patents: 4,500; 43,304). Application of aqueous ozone solutions to treat contaminated soil is difficult because of the relatively slow liquid permeation through soils and rapid decomposition of ozone. For example, if aqueous ozone is applied at a 2-atm/m pressure gradient to a soil having a permeability of 0.1 m/day (e.g., clay-loam soil), the liquid front will move only at a velocity of 0.16 m/hr. Because of these low flow velocities, practical value of aqueous ozone treatment of contaminated soils is very limited.
According to Hazen-Poiseulle's approach, if the pressure gradient is constant and the fluid compressibility is neglected, the velocity of a Newtonian fluid under capillary flow conditions is inversely proportional to the dynamic viscosity of the fluid. Then, under capillary flow conditions and ambient temperatures, air flow velocity is about two orders of magnitude (100 times) faster than that of water. The flow velocities of an ozone-oxygen or an ozone-air mixture are similar to air flow velocity. Because of rapid penetration, ozone gas, can be effectively used in soil decontamination provided the gas phase reactions can be established with organics in soils. To the knowledge of the inventor, there are no studies on the application of ozone gas to treat soils contaminated with hazardous organic wastes. According to a recent report published by the U.S. Environmental Protection Agency; U.S. Environmental Protection Agency, 1985, Remedial Action at Waste Disposal Sites (Revised), EPA/625/6-85/006, Office of Emergency and Remedial Response, U.S. EPA, Washington, D.C. pp. 9-53; "Ozone is used in the treatment of drinking water, municipal wastewater, and industrial waste, but has never been used in the treatment of contaminated soils or groundwater". This indicates that ozone, either in aqueous or gas phases, has not been used for soil decontamination. In the present invention, a pretreated gas-ozone mixture was used to decontaminate soils containing hazardous organic wastes.
It is an object of the present invention to stabilize gaseous ozone in the soil environment. It is a further object of the invention to stabilize the gaseous ozone in an efficient and cost effective manner. A further object of the invention is the efficient and expeditious decontamination of soil. Another object of the invention is to allow the in situ treatment of contaminated soil.